Control channel information transmission method, and base station and terminal using the same method

ABSTRACT

A radio communication system that includes an encoder configured to perform error correction coding for control channel information by a given error correction coding rate and a modulator configured to perform modulation of the error correction coded control channel information for transmission according to a given modulation scheme, code decimation being performed for the error correction coded control channel information prior to the modulation, and the code decimation being different according to whether Multi Input Multi Output is applied or not.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/776,927, filed on May 10, 2010, now pending, which is a continuationof U.S. application Ser. No. 12/073,086, filed on Feb. 29, 2008, nowpending, which is a continuation of International Application No.PCT/JP2005/18117, filed on Sep. 30, 2005, the contents of each areherein wholly incorporated by reference. The present application alsorelates to U.S. patent application Ser. No. 13/683,742 filed on Nov. 21,2012.

TECHNICAL FIELD

The present invention relates to a control channel informationtransmission method, and a base station and a terminal using the samemethod, and more particularly, a control channel informationtransmission method for packet communication to adaptively controlcommunication parameters using a control channel, and a base station anda terminal using the same method.

BACKGROUND ART

In a third-generation mobile communication system, an adaptive radiolink, such as adaptive modulation/demodulation, HARQ (Hybrid AutomaticRepeat Request) and scheduling, is employed to increase transmissionefficiency of data packets.

Controlling such the adaptive radio link is carried out using anindividual or common control channel, and link parameters being used ina data channel, which is transmitted substantially simultaneously withthe control channel, are reported to each user terminal.

For example, in case of an Adaptive Modulation and Coding (AMC) scheme,the control channel transmits a modulation scheme and a coding rate ofthe data channel. In case of HARQ, the control channel transmitsinformation such as the packet number of a packet to be transmitted onthe data channel and the number of retransmission times. In case ofscheduling, the control channel transmits information such as a user ID.

According to HSDPA (High Speed Downlink Packet Access) standardized in3GPP (Third Generation Partnership Protocol) for third-generation mobilecommunication systems, transmission of control information as shown inTABLE 1 is carried out by use of the common control channel calledHS-SCCH (Shared Control Channel for HS-DSCH), as described in Non-patentdocument 1.

TABLE 1 Channelization-code-set information  7 bits Modulation schemeinformation  1 bit Transport-block size information  6 bits Hybrid-ARQprocess information  3 bits Redundancy and constellation version  3 bitsNew data indicator  1 bit Ue identity 16 bits

Further, according to the above-mentioned HSDPA, when the AMC scheme isapplied in FIG. 1, illustrating the relationship between the radioenvironment and the transmission speed, under good propagation conditionin the varied radio environment I (exceeding a threshold level TH),high-speed data transmission is carried out by setting the modulationscheme to be 16QAM (Quadrature Amplitude Modulation) with an increasedcoding rate.

On the other hand, under bad propagation condition (below the thresholdlevel TH), data transmission is carried out at low speed by setting themodulation scheme to be QPSK (Quadrature Phase Shift keying) with adecreased coding rate.

As such, by changing the user transmission speed using the AMC scheme,it is carried out to maintain the quality constant. Namely, as shown inthe above FIG. 1, according to HSDPA, the modulation scheme and thecoding rate of HS-DSCH, user data, are made variable according to thepropagation condition I. Further, HS-SCCH, which is control informationrelated to the above user data, is also transmitted together with theuser data (HS-DSCH).

However, at this time, in regard to HS-SCCH, the control information, asshown in FIG. 2, illustrating the relationship between the radioenvironment and the information amount, the coding rate of errorcorrection coding for control information IV is constant, andaccordingly, irrespective of good or bad radio environment I, aninformation amount to be transmitted becomes constant.

In the above case, when the radio environment I is in good condition,quality becomes excessive to the control information for transmission.

Further, in a next-generation mobile communication system, in order torealize high-speed data transmission, multicarrier transmission and MIMO(Multi Input Multi Output) transmission using a plurality of antennasare employed. In this case, it is possible to further improve atransmission characteristic, using adaptive control of radio parameterson a subcarrier-by-subcarrier basis and on a basis of each transmissionantenna.

When the above MIMO is employed, controlling whether MIMO is to beapplied or not is carried out depending on good or bad propagationcondition I, as shown in FIG. 3. Namely, in FIG. 3 illustrating therelationship between the application or non-application of MIMO and thetransmission speed, when MIMO is applied, transmission speed becomeshigh, whereas in the opposite case, the transmission speed becomes low.

Further, formerly, the applicants of the present invention have proposedan invention of selecting one control channel format from among aplurality of control channel formats, each having a differentinformation amount, depending on a predetermined condition (whether MIMOis applied or not) in a transmission system employing MIMO, andtransmitting the control channel using the above selected controlchannel format (International Application Publication WO/2006/070466:Hereafter simply referred to as prior application.)

The above prior application is targeted on the assumed cases that thenumber of control channel information bits differs depending on whetherMIMO is applied or not. As a prerequisite, the number of informationbits IV is increased when MIMO is applied (period III) for user data asshown in FIG. 4, while the number of information bits is decreased whenMIMO is not applied for user data, as shown in FIG. 5.

Accordingly, as shown in FIG. 6 illustrating the relationship betweenthe MIMO application and the control channel information amount, in theperiod III of the propagation environment I in which MIMO is applied,there is a problem that the number of variable parameters increases, andthe number of information bits required for the control channelincreases. Further, when the number of simultaneous multiplex users in asingle frame increases, there is a problem that the control channelinformation also increases in proportion to the number of users.

NON-PATENT DOCUMENT 1]

3GPP TS 25.212 V5.9.0 (2004-06)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Accordingly, the present invention is focused to solve theaforementioned problems in packet-type data transmission in which theAMC (Adaptive Modulation and Coding) scheme is applied, by makingvariable the coding rate in the error correction coding on HS-SCCH, thecontrol channel information.

Means to Solve the Problems

As a first aspect of the present invention to solve the aforementionedproblems, a control channel information transmission method includes:performing error correction coding for control channel information basedon an Adaptive Modulation and Coding scheme; by using a predeterminedmodulation scheme, modulating and transmitting the error correctioncoded control channel information; and further, according to propagationcondition, differentiating a coding rate in the error correction coding.

Further, as a second aspect of the present invention to solve theaforementioned problems, a control channel information transmissionmethod includes: with a constant coding rate, performing errorcorrection coding for control channel information based on an AdaptiveModulation and Coding scheme; by using a predetermined modulationscheme, modulating and transmitting the error correction coded controlchannel information; and further, prior to the modulation, performingcode decimation or code repetition of the error correction coded signal,according to propagation condition.

Still further, as a third aspect of the present invention to solve theaforementioned problems, a control channel information transmissionsystem based on an Adaptive Modulation and Coding scheme includes: onthe base station side, an error correction coding unit performing errorcorrection coding for control channel information; and a modulation unitmodulating a coded output of the error correction coding unit with apredetermined modulation scheme. Further, it is configured that codingrates in the error correction coding unit are differentiated accordingto propagation conditions.

Further, in the aforementioned aspects, the coding rate of the controlchannel when Multi Input Multi Output is applied is set larger than thecoding rate when Multi Input Multi Output is not applied, so that thenumber of transmission code bits becomes constant irrespective ofwhether Multi Input Multi Output is applied or not.

In the aforementioned aspects, on the receiving side, error correctiondecoding for a commonly received signal is performed by respective errorcorrection decoding units corresponding to coding rates differentiatedaccording to the propagation condition, and further, likelihood in theerror correction decoded signal is decided, and based on the likelihooddecision result, an error correction decoded signal being decided to bevalid is output.

The features of the present invention will become apparent by theembodiments of the invention described according to the accompanieddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram illustrating relationship between a radioenvironment and a transmission speed in the AMC control of HS-DSCH ofHSDPA, as the prior art.

FIG. 2 shows a diagram illustrating relationship between a radioenvironment and an information amount in HS-SCCH of HSDPA, as the priorart.

FIG. 3 shows a diagram illustrating relationship between a radioenvironment and a transmission speed in HS-DSCH in which MIMO isapplied, in the prior application.

FIG. 4 shows a diagram illustrating an example of a control channelformat when MIMO is applied.

FIG. 5 shows a diagram illustrating an example of a control channelformat when MIMO is not applied.

FIG. 6 shows a diagram illustrating relationship between a radioenvironment and an information amount in HS-SCCH when MIMO is applied.

FIG. 7 shows a configuration block diagram of a transmission systemincluding a base station 1 and a user terminal 2 in which the presentinvention is applied.

FIG. 8 shows a diagram illustrating a configuration of a control channelgeneration section 12, corresponding to the invention of the priorapplication.

FIG. 9 shows a diagram illustrating a first exemplary configuration ofcontrol channel generation section 12, according to the presentinvention.

FIG. 10 shows a diagram illustrating relationship between application ofMIMO and a control channel information amount, when the presentinvention is applied.

FIG. 11 shows a diagram illustrating another exemplary configuration ofcontrol channel generation section 12, according to the presentinvention.

FIG. 12 shows an exemplary configuration of a control channeldemodulation section in a user terminal, according to the presentinvention.

FIGS. 13A & 13B show a diagram illustrating an effect, as compared withthe case of employing the invention of the prior application.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the embodiments of the present invention are describedreferring to the drawings.

FIG. 7 shows a configuration block diagram of a transmission systemincluding a base station 1 and a user terminal 2 in which the presentinvention is applied. In particular, the present invention has a featurein the configuration of the embodiment of a control channel generationsection 12.

In regard to downlink control channel transmission from a base station 1to a user terminal 2, the feature of the present invention is describedusing the embodiment of the prior application in which MIMO is applied.However, the application of the present invention is not limited to thetransmission system configuration shown in FIG. 7.

A format selection/assignment section 10 in base station 1 selects acontrol channel format, based on information including the number ofmultiplex users, transmission/reception function of the user terminal,downlink QoS and downlink CQI (Channel Quality Indicator).

Here, examples of the control channel formats to be selected are asshown earlier in FIG. 4(TABLE 2) and FIG. 5(TABLE 3).

A control format A shown in FIG. 4 includes modulation scheme (antenna1)—modulation scheme (antenna 4), coding rate, spreading factor and codeset, as adaptive control parameters. For example, in modulation scheme(antenna 1)—modulation scheme (antenna 4), four (4) modulation schemetypes (QPSK, 8PSK, 16QAM, 64QAM) are set as a variable range. In theabove control channel format A shown in TABLE 2, the types of adaptiveparameters and the variable range are wide, and for example, themodulation scheme can be varied on an antenna-by-antenna basis at thetime of MIMO transmission.

Meanwhile, a control format B shown in FIG. 5 includes modulation scheme(common to antennas), coding rate, spreading factor and code set, asadaptive control parameters. For example, in the modulation scheme(common), two modulation scheme types (QPSK, 16QAM) are set as avariable range. In the above control channel format B shown in TABLE 3,as compared with the control channel format A, the types and thevariable range of the adaptive control parameters are limited, and thenumber of bits is approximately ½ of the control channel format A.

Referring back to FIG. 7, information representing the assignment of thecontrol channel format selected in format selection/assignment section10 is reported from a signaling generation section 11 to user terminal2, via a selector 15 and a transmitter 16, as signaling information.Also, the format assignment information is reported to control channelgeneration section 12 and a data channel generation section 13.

Control channel generation section 12 is a featured portion of thepresent invention, and has different configurations and functionscorresponding to the embodiments described later, and however, as abasic configuration, the configuration includes an error correctioncoding unit and a modulation unit.

The control channel and the data channel, generated in control channelgeneration section 12 and data channel generation section 13, aremultiplexed in a multiplexing section 14 based on the format assignmentinformation, and thereafter, transmitted via a downlink to user terminal2, through transmitter 16.

A signaling demodulation section 22 in user terminal 2 demodulates thesignaling information (format assignment information) reported from basestation 1 through a receiver 20, and reports a downlink control channelformat to a control channel demodulation section 23. Control channeldemodulation section 23 demodulates the control channel based on thedownlink control channel format reported from signaling demodulationsection 22. Control channel demodulation section 23 reports downlinkadaptive control parameters demodulated from the control channel, to adata channel demodulation section 21.

Data channel demodulation section 21 performs demodulation of the datachannel, using the adaptive control parameters reported from controlchannel demodulation section 23.

The downlink CQI for use in selecting the downlink control channelformat is measured by a propagation path measurement section 24 in userterminal 2. The downlink CQI is transmitted to base station 1, throughthe uplink control channel from user terminal 2 to base station 1,together with the uplink QoS and the transmission/reception function ofuser terminal 2.

Next, uplink control channel transmission from user terminal 2 to basestation 1 will be described.

Similar to the downlink control format, an uplink control channel formatis selected in format selection/assignment section 10 of base station 1.To select the uplink control channel format, information sets includingthe number of multiplex users, the transmission/reception function ofthe user terminal, uplink QoS, uplink CQI (Channel Quality Indication),etc. are used.

The selected uplink control format is reported from signaling generationsection 11 to user terminal 2, via selector 15 and transmitter 16, assignaling information. Signaling demodulation section 22 demodulates thesignaling information reported from base station 1, decides theassignment (multiplexing method) of the control channel and the datachannel on the uplink, and reports the above format assignmentinformation to a control channel generation section 25 and a datachannel generation section 27.

In base station 1, the uplink control channel format selected by formatselection/assignment section 10 is reported to a control channeldemodulation section 18 for the uplink.

Control channel demodulation section 18 demodulates the control channel,based on the uplink control channel format reported from formatselection/assignment section 10. Control channel demodulation section 18reports the demodulated uplink adaptive control parameter to a datachannel demodulation section 19.

Data channel demodulation section 19 performs demodulation processing ofthe data channel, using the adaptive control parameter reported fromcontrol channel demodulation section 18. The uplink CQI for use inselecting the uplink control channel format is measured by a propagationpath measurement section 17 in base station 1.

Additionally, the measured uplink CQI is report from propagation pathmeasurement section 17 to format selection/assignment section 10. Also,the uplink QoS, the downlink CQI and the transmission/reception functionof user terminal 1, transmitted to base station 1 through the uplinkcontrol channel from user terminal 2 to base station 1, are transmittedto format selection/assignment section 10.

Next, in FIG. 7, an exemplary configuration of control channelgeneration section 12 featuring the present invention will be described.Here, in the prior application, there has been assumed a case ofapplying MIMO, in which the number of control channel information bitsdiffers depending on whether MIMO is applied or not, as shown in FIG. 4and FIG. 5.

Namely, from among a plurality of control channel formats, one controlchannel format is selected and used so that the number of controlchannel information sets is large when MIMO is applied for user data(refer to FIG. 4), while the number of control channel information setsbecomes small when MIMO is not applied for user data (FIG. 5).

In the above case, the configuration of control channel generationsection 12 becomes as shown in FIG. 8.

There are provided an error correction coding unit 120 and a modulationunit 121. Error correction coding is performed in error correctioncoding unit 120, and corresponding thereto, error correction decoding isperformed in control channel demodulation section 23 on the userterminal 2 side.

Now, let a coding rate R to be as R=0.241, where R is a ratio of thenumber of code information bits to be transmitted to the number oftransmission code bits obtained by the error coding thereof. When MIMOis not applied in FIG. 8, the number of code information bits in a frameto be transmitted is 68, while the number of transmission code bitsbecomes 282=(68×1/0.241) bits.

Meanwhile, when MIMO is applied, if the number of code information bitsin a frame to be transmitted is 141, the number of transmission codebits becomes 585=(141×1/0.241) bits.

As such, because of a fixed coding rate, there is a problem that thenumber of transmission code bits becomes large when MIMO is applied, asshown in FIG. 6.

Accordingly, the object of the present invention is to solve the aboveproblem.

FIG. 9 shows a diagram illustrating a first exemplary configuration ofcontrol channel generation section 12, according to the presentinvention. Similar to the configuration shown in FIG. 8, control channelgeneration section 12 includes error correction coding unit 120 andmodulation unit 121.

A feature different from the configuration shown in FIG. 8 is that thecoding rate in error correction coding unit 120 is made variable.

A case of a large coding rate is weak against a propagation path error,while a case of a small coding rate is strong against a propagation patherror. Meanwhile, MIMO is applied when there are few propagation errors,and MIMO is not applied when there are frequent propagation errors.

Therefore, according to the present invention, when MIMO is applied foruser data, the coding rate of the error correction coding unit forgenerating the control channel is increased. To the contrary, when MIMOis not applied for user data, the coding rate of the error correctioncoding unit for generating the control channel is reduced.

As an embodiment, when MIMO is applied for user data, the coding rate oferror correction coding unit 120 in control channel generation section12 is set to be 0.5.

By this, the number of the transmission code bits becomes 282(=141÷0.5), while when MIMO is not applied for user data, as in theexemplary case shown in FIG. 8, the coding rate in error correctioncoding unit 120 is set to be 0.24, and thus, 282 (=141÷0.5) bits aretransmitted.

By this, irrespective of whether MIMO is applied or not, the number oftransmission code bits becomes identical, and it becomes possible toobtain constant control information quality without wasting radioresources.

FIG. 10 shows a diagram illustrating relationship between application ofMIMO and a control channel information amount when the present inventionis applied. As compared with FIG. 6, even when MIMO is applied, it ispossible to make constant the number of transmission code bits of errorcorrection coding. Thus, it is possible to prevent resources from beingwasted.

FIG. 11 shows a diagram illustrating another exemplary configuration ofcontrol channel generation section 12, according to the presentinvention. In this embodiment, there is a feature that a unit 122 whichselectively applies a puncture function or a repetition function isprovided between error correction coding unit 120 and modulation unit121.

Namely, according to the present embodiment, the coding rate of errorcorrection coding unit 120 is made constant irrespective of whether MIMOis applied or not. Meanwhile, it is configured to vary the coding ratein an equivalent manner, by providing unit 122, having the puncturefunction or the repetition function, on the output side of errorcorrection coding unit 120.

With this, the coding rate is made variable on the input side ofmodulation unit 121, which has the same signification as theconfiguration of control channel generation section 12 shown in FIG. 9.

Now, in case the puncture function is provided, by means of the puncturefunction, unit 122 performs decimation processing of the output data oferror correction coding unit 120 at certain intervals, when MIMO isapplied. When MIMO is not applied, the output data of error correctioncoding unit 120 is made to pass through without being changed. By this,irrespective of MIMO application, the bit counts when the output oferror correction coding unit 120 is input to modulation unit 121 is madeto be identical.

Also, when the repetition function is provided, by means of therepetition function, unit 122 repetitively outputs identical bits of theoutput data of error correction coding unit 120, when MIMO is notapplied. In this case also, it is possible to make the number oftransmission bits when MIMO is not applied substantially identical tothe number of transmission bits when MIMO is applied.

FIG. 12 shows yet another embodiment of the present invention. In thetransmission system shown in FIG. 7, as a function of signalinggeneration section 11 in base station 1, the application ornon-application of MIMO and a format in control channel generationsection 12 are reported. The embodiment shown in FIG. 12 makes the abovefunction of signaling generation section 11 unnecessary.

Namely, in user terminal 2, the receiving side, reception is made usingtwo control channel format types corresponding to the cases when MIMO isapplied and not applied. Then, from the received data, any one formatwhich appears to be correct is detected. With this, base station 1, thetransmitting side, can report to the receiving side the application ornon-application of MIMO, without using an information bit resource forreporting the application or non-application of MIMO.

In control channel demodulation section 23 shown in FIG. 12, there areprovided two error correction decoding units 231a, 231 b, respectivelycorresponding to the above-mentioned two control channel format types,on the output side of a demodulator 230 for demodulating signalstransmitted from the base station 1 side, without signalingdemodulation.

The first error correction decoding unit 231 a can obtain a correctoutput when performing error correction decoding to a frame signalhaving the number of bits of 68 when MIMO is not applied. For thispurpose, error correction decoding unit 231 a performs error correctiondecoding, based on an assumed coding rate=0.24.

Meanwhile, the second error correction decoding unit 231 b can obtain acorrect output when performing error correction decoding to a framesignal having the number of bits of 141 when MIMO is applied. For thispurpose, error correction decoding is performed on the basis of anassumed coding rate=0.5.

From the outputs of the first and the second error correction decodingunits 231 a, 231 b, a reliability decision & selection unit 232 decideswhich decoding result appears to be correct, and selects the output ofeither one side of error correction decoding units 231 a, 231 b, basedon the above result.

By this, it is possible to save an information bit resource forreporting the application or non-application of MIMO.

FIGS. 13A and 13B show a diagram illustrating an effect, as comparedwith the case of employing the invention of the prior application.

FIG. 13A shows transmission power ratio from the base station usingHSDPA. The remaining power not shown in FIG. 13A corresponds to thepower assigned to traffic channels.

FIG. 13B shows the power usable in the traffic channels obtained fromFIG. 13A, on the basis of the number of channels in HS-SCCH. Asdescribed earlier, according to the invention in the prior application,the coding rate of HS-SCCH is constant even when the information amountbecomes large. The power available for the traffic channels becomesdifferent, depending on whether MIMO is applied or not (refer to III inFIG. 13B). In contrast, according to the present invention, the abovepower becomes constant (refer to IV in FIG. 13B).

For example, in case that the traffic channels are two channels (shownby the arrow in FIG. 13B), the effect of the present invention in termsof the power is 1.5 times as great as compared with the invention in theprior application.

INDUSTRIAL APPLICABILITY

As having been described according to the drawings, by making the codingrate of error correction coding variable according to the controlchannel mode in the present invention, it becomes possible to maintainthe transmission quality constant, irrespective of a good or badpropagation condition, and also, even when MIMO is applied, it becomespossible to prevent excessive quality to the transmission of controlinformation bits.

What is claimed is:
 1. A radio communication system comprising: anencoder configured to perform error correction coding for controlchannel information by a given error correction coding rate; a modulatorconfigured to perform modulation of the error correction coded controlchannel information for transmission according to a given modulationscheme, code decimation being performed for the error correction codedcontrol channel information prior to the modulation, and the codedecimation being different according to whether Multi Input Multi Outputis applied or not.